1. Field of the Invention
The present invention relates to an X-ray detection apparatus and, more particularly, to an information processing technique for setting information indicating the direction of a transmission image of an object in a radiographed image.
2. Description of the Related Art
Recently, in the field of X-ray image diagnosis apparatuses for medical uses, digital apparatuses using digital images have become popular in place of analog apparatuses using conventional X-ray films and intensifying screens.
A digital X-ray image diagnosis apparatus has the advantage of being capable of displaying radiographed images obtained by continuous X-ray imaging on a monitor, as moving images and storing them in a storage device such as a semiconductor memory or hard disk.
In both analog and digital systems, it is important for X-ray image diagnosis apparatuses to record in advance information indicating the direction of a transmission image of an object (to be referred to as an “object direction” hereinafter) in a radiographed image in association with the radiographed image.
A radiographed image obtained by an X-ray image diagnosis apparatus is a transmission image of an object. For this reason, if the direction in which the object faced relative to the X-ray detection apparatus during radiography cannot be determined, a doctor or other viewer may confuse (for example) the vertical and horizontal directions at the time of diagnosis.
Assume that X-ray imaging is performed on a person's chest as the object. In this case, an X-ray detection apparatus may be placed to the rear of the object, to irradiate the object with X-rays from the front of the object, or the X-ray detection apparatus may be placed in front of the object, to irradiate the object with X-rays from the rear of the object. In this case, the horizontal direction of a transmission image of the object in an obtained radiographed image reverses depending on the manner in which the X-ray imaging has been performed.
In addition, when X-ray imaging is to be performed on a portion of the body of a patient lying on a bed, the vertical direction of a transmission image of the object in an obtained image reverses depending upon the direction in which the patient's head is placed relative to the X-ray detection apparatus.
For this reason, in existing circumstances, X-ray imaging is performed using a marker for the discrimination of an object direction. This operation will be described in detail with reference to FIGS. 15A and 15B. FIG. 15B shows a radiographed image group obtained by X-ray imaging in various directions for an object 1501 attached with a marker by using an X-ray detection apparatus 1502 shown in FIG. 15A.
As shown in FIG. 15A, in general, a member made of a metal such as lead (to be referred to as a lead marker) which does not transmit X-rays is used as a marker, and a vertically and horizontally asymmetric symbol such as “L” or “R” is used. X-ray imaging is performed after the lead marker is attached to the object 1501 (or the X-ray detection apparatus 1502). With this operation, the radiographed image contains an image of the lead marker. This allows a doctor or other viewer to discriminate the object direction at the time of diagnosis.
FIG. 15A exemplifies a case in which X-ray imaging is performed on a person's chest. In this case, the obtained radiographed image is generally one of the eight types of images 1500a to 1500h shown in FIG. 15B.
On the other hand, with the widespread use of digital X-ray image diagnosis apparatuses, radiographed images are displayed on monitors mounted on X-ray image diagnosis apparatuses in more cases. In general, digitized radiographed images (radiographed image data) obtained by digital X-ray image diagnosis apparatuses are easy to process.
For this reason, a digital X-ray image diagnosis apparatus uses a method of embedding information (a symbol or graphic pattern) indicating an object direction in radiographed image data by performing so-called digital image processing after X-ray imaging.
According to this method, a doctor or other viewer determines an object direction by seeing the relative positions of the object and X-ray detection apparatus at the time of X-ray imaging, and manually sets the determination result.
It is, therefore, important for this method to minimize determination errors concerning object directions. In an X-ray image diagnosis apparatus or the like in which an X-ray detection apparatus is permanently installed on a dedicated bed or the like, some contrivance is made to always set the head of the patient in a specific direction relative to a bed. This makes the object direction always remain the same, and hence can reduce determination errors made by a doctor or other viewer when determining an object direction.
There has also been provided a method of automatically determining an object direction by extracting geometrical features of a transmission image of each region such as an organ, bone, or contour from a radiographed image by performing image processing for radiographed image data after X-ray imaging. This method automatically sets a determined object direction, and hence can minimize setting errors at the time of setting of determination results.
In addition, Japanese Patent Laid-Open No. 2004-97543 proposes an arrangement in which the radiographed image display unit of a digital X-ray image diagnosis apparatus is placed parallel to an X-ray detection apparatus through an object. This arrangement facilitates the determination of an object direction, and can reduce determination errors.
The various methods described above have various problems. For example, in the method of performing X-ray imaging for an image of a lead marker or the like, a character like “L” or “R” is used as a symbol. This may cause a placement error or read error due to a misjudgment or carelessness.
On the other hand, consider the method of making a doctor or the like determine an object direction by seeing the relative positions of an object and X-ray detection apparatus and embedding a symbol or graphic pattern corresponding to the determination result by so-called digital image processing. This method is free from the problem concerning marker placement errors, read errors, and the like. However, the method cannot avoid the possibility that a symbol or graphic pattern indicating an object direction may be set erroneously due to a determination error caused by a misjudgment by a doctor or other user, a setting error caused by carelessness, or the like.
For an object which is difficult to move to an X-ray room or sit up from the bed, X-ray imaging is performed after a transportable X-ray detection apparatus is installed depending on the object. In this case, the installation position of the X-ray detection apparatus changes for every X-ray imaging. This further increases the possibility of the occurrence of a determination error at the time of determination of an object direction and an input error at the time of setting of a determination result.
On the other hand, consider the method of automatically setting information indicating an object direction based on an estimation result obtained by automatically estimating an object direction upon extracting geometrical features of an image of a region such as an organ, bone, or contour by image processing of a radiographed image. This method is free from the problem of setting errors. The method, however, cannot accurately estimate an object direction concerning an object having a physical abnormality such as heterotaxy. That is, the method cannot prevent estimation results from containing estimation errors, and hence cannot be used without careful consideration.